1. Field of the Invention
Embodiments of the present invention relate generally to a pipeline pig that is propelled by the pressure of a pipeline fluid flowing through a pipeline. In particular, embodiments of the invention relate to a pipeline pig with a plurality of distinct flow channels extending therethrough that selectively permit and prohibit flow of the pipeline fluid through the pipeline pig.
2. Description of the Related Art
An instrument for inspecting, cleaning, and maintaining a pipeline is often referred to as a pipeline pig. In some applications, the pipeline pig is propelled along an interior of the pipeline under the pressure of a pipeline fluid flowing through the pipeline. To facilitate advancement of the pipeline pig, one or more flexible guide disks or cups are often provided that extend outwardly from a longitudinal body of the pipeline pig. The flexible guide disks extend to an interior wall of the pipeline so as to form a seal between the pipeline and the pipeline pig. If the seal is substantially complete, the pipeline pig is induced to travel at the speed of the pipeline fluid. In some applications, flow channels are provided through the pipeline pig to permit a portion of the pipeline fluid to flow through the pipeline pig, thereby regulating the speed of the pipeline pig.
Buildup of debris within the pipeline can be problematic for the operation of the pipeline pig. Debris ahead of the pig may slow the pipeline pig below a minimum speed required for carrying out the desired application, or in some instances, can completely prevent the pipeline pig from moving forward through the pipeline. Also, flow channels for regulating a speed of the pipeline pig reduce the maximum fluid force that can be applied to the pipeline pig to drive it through the pipeline, and thus can increase the likelihood that the pipeline pig will become stuck in the pipeline when debris or other obstructions are encountered. If the pipeline pig becomes stuck in the pipeline, flow of the pipeline fluid can be restricted or impeded. Often, contingency plans to recover the pipeline pig include cutting the pipeline at the point where the pig is stuck in order to remove it. Once the pig is removed, the pipeline is then reconnected and put back in service. This contingency plan is costly due to inhibited pipeline flow and downtime while the pipeline is cleared.